Mooney_Driver wrote:
Probably the best solution is indeed to fly to the minimum and then keep the rate of descent you had on the glide.
IIRC, that’s what autoland systems do.
That’s exactly what happened to me once.
Except I didn’t write that 
I wrote: Would you get zero-zero conditions and a loss of GPS and a loss of radio (precluding a PAR approach) and a loss of ILS?
You obviously can’t and shouldn’t follow it to touchdown
I tried this once (in VMC, at Norwich) and it worked all the way down. I believe it is not supposed to but on that occassion it took me all the way down. Many years ago.
Peter wrote:
I tried this once (in VMC, at Norwich) and it worked all the way down. I believe it is not supposed to but on that occassion it took me all the way down. Many years ago.
It might work or it might not. There is no requirement on the quality of the ILS glidepath once you’re past the minimum.
I’m not sure if it’s a feature of the approach design or the avionics, but on most of the LPVs I’ve seen, the guidance will “flatten” and follow a horizontal trajectory a few (10? 50?) feet above the runway.
Noe wrote:
the guidance will “flatten” and follow a horizontal trajectory a few (10? 50?) feet above the runway.
I have played with this on the sim, and it closer to 10’ than 50’. Also, once you are past the end of the runway, it climbs away.
Airborne_Again wrote:
IIRC, that’s what autoland systems do.
IIRC they do employ more than just that, amongst which Radio Alt. Flare mode works in a function of terrain closure which is taken from Radio Altitude.
JasonC wrote:
You obviously can’t and shouldn’t follow it to touchdown
I understand LPV approaches allow you to pretty much do that. When my plane was flight tested in full VMC of course after the installation of AP and the WAAS equipment, the test crew tried how the AP would behave and found they could go down all the way to the touchdown zone in a totally stable glidepath. The disconnected just before touch down.
So I reckon this might actually be a very good “rescue” superior to an ILS.
I was not aware of the “flattening” of the LPV GS, this is very interesting. In theory this would mean if flown by AP it would round out just above the runway and all you’d have to do is gradually reduce the throttle while holding pitch… from 10 ft, this should result into a managable touch down. I wonder if newer AP systems could really start using this kind of thing for GA Autoland systems. It certainly does not appear to be so far off.
One question I am musing about is whether synthetic vision on your PFD would be a true help or actually a dangerous temptation… Is it really accurate enough to “see” the runway or not. Clearly, a HUD System with synthetic vision would be top for that. I recall that airlines like Southwest operated handflown CAT III on their 737’s for years with the HUD.
Mooney_Driver wrote:
In theory this would mean if flown by AP it would round out just above the runway and all you’d have to do is gradually reduce the throttle while holding pitch… from 10 ft, this should result into a managable touch down.
That is exactly how it works in the sim. Any volunteers to see if it works in reality?
from 10 ft, this should result into a managable touch down.
I wonder if this “bend upwards at 10ft” is actually nothing to do with LPV but just the behaviour of the particular autopilot when it has lost vertical guidance because the GS has become flagged as invalid?
Peter wrote:
I wonder if this “bend upwards at 10ft” is actually nothing to do with LPV but just the behaviour of the particular autopilot when it has lost vertical guidance because the GS has become flagged as invalid?
I suspect not, because it climbs away at the far end of the runway.
Any volunteers to see if it works in reality?
In VMC and with preparation why not. They flew it down to about 20 ft and it was dead center and right before the touchdown marker when they disconnected.
Realistically you would need to know it works down to say 50 ft and 99% of the time you would be able to land after that. That would correspond to about 200 to 300m RVR. And in our planes you are at a much lower vantage point than in any airliner.
